Electric lamp filament



Sept. 23, 1969 N. B. AGDUR ETAL ELECTRIC LAMP FILAMENT Original Filed March 16, 1964 INYENTORE United States Patent 3,468,006 ELECTRIC LAMP FILAMENT Nils Bertil Agdur, Danderyd, Florian Sellberg, Djursholm, Kurt Goran Rafael Boling, Taby, and Karl Yngve Ohman, Stockholm, Sweden, assignors to Kooperativa Forbundet Ekonomisk Forening, Stockholm, Sweden, a corporation of Sweden Original application Mar. 16, 1964, Ser. No. 352,121, now Patent No. 3,361,924, dated Jan. 2, 1968. Divided and this application May 1, 1967, Ser. No. 645,087 Claims priority, application Sweden, Mar. 21, 1963, 3,069/ 63 Int. Cl. 1101 9/16, 9/44 US. Cl. 29-2518 6 Claims ABSTRACT OF THE DISCLOSURE The method for forming a light producing element for incandescent electric lamps and the like and having a roughened and textured light-emitting surface, in which an electrically conductive elongated element is formed with a surface having protrusions and/or depressions wherein the differential surface height and/or the spaces between the protrusions and/ or depressions, is generally of the same order of magnitude as the wave length of visible light radiation produced upon energization of said element.

This application is a division of co-pending application S.N. 352,121, filed Mar. 16, 1964, now Patent No. 3,361,924.

This invention relates to light-emitting elements or filaments as used in incandescent electric lamps and the like for producing or emitting visible light radiation and, more particularly, to such elements or filaments which include a large plurality of light-emitting points or sources for enhanced efiiciency and increased emission of light.

As will be understood, visible light radiation is conventionally produced in incandescent lamps by thermic radiation as an electric current is passed through a filament or wire heating it to incandescence. A wide variety of materials is available and has been used for such incandescent filaments, as well as a wide variety of configurations of the wires or filaments as supported within the enclosing envelope of the lamp bulb. Regarding generally metallic filaments, such as fine tungsten wire, etc., even though such filaments have been arranged or disposed within the lamp bulb in coiled or curled or helical or other irregular configurations, still the thin wire from which the filament is formed has had a relatively smooth surface or a surface generally as smooth as is conventionally produced in the formation of the thin filament wire in the first place.

According to this invention, however, there are provided filament wires and ribbons and like arrangements for use as the incandescent filament in an electric lamp, but having on the light-emitting surface thereof a large plurality of ridges and depressions or outwardly extending points or crystal protrusions or other rough or textured surface configurations whereby the light-emitting output is substantially increased as the individual ridges or depressions in the rough surface all form an increased plurality of individual light-emitting sources or elements upon the electric energization of the filament. As a further feature of this invention, and for further enhancement of the results obtained, such ridges and depressions or other roughened or textured nature of the lightemitting surface are formed and provided so that the extending height of a ridge or depth of a depression, with respect to the average level of the roughened or textured 'ice surface, and/or the distance between such elements is dimensioned of generally the same order of magnitude as the wave length of the light radiation desired.

With the foregoing and additional objects in view, this invention will now be described in more detail, and other objects and advantages thereof will be apparent from the following description, the accompanying drawings, and the appended claims.

In the drawings, in which several embodiments in accordance with and for practicing this invention are illustrated in highly schematic or diagrammatic form and greatly exaggerated because of the tiny dimensions actually utilized:

FIG. 1 illustrates a portion of an incandescent filament wire embodying and for practicing this invention and having a large plurality of ridges and depressions on the surface thereof;

FIG. 2 is a transverese section along the line 2-2 of FIG. 1;

FIG. 3 is a diagrammatic showing of one manner of producing the filament wire of FIG. 1;

FIG. 4 is a further embodiment of this invention illus trating a metallic ribbon as an incandescent filament and carrying on the surface thereof a large plurality of point sources as sintered powder; and

FIG. 5 is a further embodiment of this invention illustrating an incandescent filament as a metallic ribbon, the surface of which has been etched to separate or delineate individual crystals or crystal lattices.

Referring to the drawings, in which like reference characters, indicate like parts throughout the several views thereof, there is indicated in FIG. 1 a small section of tungsten filament wire 10 carrying on the surface thereof a large number of axial ridges 11 and grooves therebetween, all indicated by the axial lines in FIG. 1 and around the transverse section of FIG. 2.

As further indicative of this surface arrangement (which is difficult to illustrate realistically merely by drawings), one satisfactory method for producing the desired configuration is schematically illustrated in FIG. 3. Thus, a die 15 is shown having a drawing orifice 16 therein of substantially the same diameter as the diameter of wire 10 (which may satisfactorily be conventional tungsten incandescent lamp filament wire). The upper portion 17 of orifice 16 has a slightly flared configuration in which is deposited a supply of diamond powder indicated at 18. In this manner, as wire 10 is drawn downwardly through orifice 16 in die 15, diamond powder 18 will form in the surface thereof the various axial grooves and ridges therebetween as indicated in FIGS. 1 and 2.

As will be understood, although ridges '11 may be regular and symmetrical in disposition on the outer surface of wire 10, this is not necessary for satisfactory results here, a more or less random-disposition being satisfactory. Preferably, the height of ridges 11 and depth of the recesses or grooves therebetween, when measured from the average level of the roughened surface, is generally of the same order of magnitude as the wave length of the light radiation desired to be producede.g., within the range of about 1-2 microns for light in optical range. Similarly, as will be understood, such dimensioning of the ridges and grooves in wire 10 is readily and simply obtained by the selection of grain size for diamond powder 1% so that, upon drawing wire 10- through orifice 16 in die 15 against the diamond powder, a proper or satisfactory dimensioning of the roughened or textured surface is obtained as controlled by the grain size of the powder. When produced in this manner, of course, the widths and distances between adjacent ridges or recesses =11 will be generally of the same order of magnitude as the radial extents thereof as defined by the grain size of diamond powder and as preferred in accordance herewith, thereby enhancing the effect.

Referring now to an additional embodiment or arrangement for practicing this invention as illustrated in FIG. 4, there is provided a ribbon or strip filament 20 of an appropriate incandescent light filament material (such as high-resistance or refractory metals, tungsten, molybdenum, platinum, etc.) onto the light-emitting surface of which are afiixed (satisfactorily by sintering) metallic light-emitting powder granules indicated at 21 to form a great plurality of light-emitting points or sources. For example, satisfactory results in accordance herewith are achieved with this embodiment of the invention by sintering, in known manner, fine powdered tungsten granules to the surface of a tungsten ribbon such as 20 and adapted for use as an incandescent filament.

As will be understood from the foregoing, the grain size of the powdered material indicated at 21 is specifically selected so that, as sintered upon the light-emitting surface of ribbon 20, the height of the various point sources of powder granules approaches or is generally of the same order of magnitude as the wave length of the radiation desired to be produced thereby. Thus, as with the embodiment described before, the effective lightemitting surface of filament 20 is increased and the efficiency and light emission therefrom is also increased by the large plurality of point sources provided by the powder granules sintered onto the surface of ribbon 20. As will also be understood, instead of point sources on the surface of an incandescent filament as in FlG. 4 and instead of cutting grooves into the surface of a filament wire to form ridges as in FIGS. 1-3, ridges may be applied to an otherwise smooth filament surface as by sintering or otherwise, in accordance herewith, and preferably, under circumstances where the width of the ridges and the grooves therebetween, as well as the height and/ or depth thereof all are produced as approximating or generally of the same order of magnitude as the wave length of the light desired to be emitted thereby.

A further embodiment of an incandescent filament structure arranged in accordance herewith is illustrated in FIG. 5 as comprising a rolled tungsten (or other appropriate metal) ribbon 30, the light-emitting surface of 'which has been polished and etched (somewhat in the manner of preparing metallic specimens for microscopic metallographic or crystallographic inspection) whereby individual crystal forms or lattices in the metallic microstructure are somewhat isolated or separated (as indicated by the random shapes shown as 31). As will be understood by men skilled in this art, an etched pattern generally of the random form indicated in FIG. 5 is readily obtained by such techniques applied to rolled tungsten or other metal ribbons, with the random lines defining the areas 31 representing etched recesses formed at the junctures between crystals or crystal forms of substantially the same orientation within the surface of the rolled metal strip. Also as well understood in the metallurgical arts, the particular sizes of such crystals or crystal forms which may be separated by etching are readily determinable by well known techniques in the heat treatment of such a rolled metal ribbon, so that the number of such randomly shaped and spaced crystallographic areas 31 per unit length of ribbon 30 may be satisfactorily increased or decreased as desired. With this embodiment, as with those previously described, each of the irregularly and randomly shaped crystollographic areas 31 forms a source of light-emitting surface, upon energization of the ribbon 30, in much the same manner in accordance herewith as the powdered granules of the embodiment of FIG. 4 and/or the axial ridges of the embodiment of FIG. 1.

Similarly, as with the foregoing embodiments, the depth of etch is preferably of the same order of magnitude as the wave length of the light desired to be emitted thereby.

Accordingly, there are provided herewith a variety of enhanced and novel filament arrangements or light source elements for inclusion into incandescent lamps and like devices to produce emission of radiation upon energization as by an electric current, and under circumstances where the efficiency and the total emission is enhanced by the provision on the light-emitting surfaces of such filaments or elements a large plurality of ridges or points or separated areas or recesses, all of which together provide a large plurality of light-emitting sources. Similarly, in the various instances noted, the heights (or depths) of said sources with respect to the average level of filament surface is correlated with and approximates or, at least, is generally of the same order of magnitude as the wave lengths of the radiation desired to be emitted thereby. In this connection, the term average level used above refers to the surface level of the wire or ribbon, etc., under ocular observation and without respect to the surface changes caused by the noted ridges or grooves or points.

Similarly, although several satisfactory metal materials have been mentioned above, a variety of appropriate resistant and refractory metals give saisfactory results in accordance herewith, and includes those metals, conventionally used for incandescent lamp filaments-e.g., tungsten, molybdenum, platinum, tantalum.

While the illustrative embodiments disclosed above form preferred embodiments of this invention, this invention is not limited to these precise illustrative embodiments, and changes may be made therein without departing from the scope of this invention which is defined in the appended claims.

What is claimed is:

1. In a method for forming a light-producing element for incandescent electric lamps and the like having a roughened and textured light-emitting surface, the steps which comprise forming an electrically conductive elongated filament adapted to emit light upon energization thereof, treating the surface of said filament for producing thereon a large plurality of tiny protrusions spaced over said surface, the heights of said protrusions being generally of the same order of magnitude as the wave length of the visible light radiation produced upon energization of said element.

2. In a method for forming a light producing element for incandescent electric lamps and the like having a roughened and textured light-emitting surface, the steps which comprise forming a metal filament wire, introducing said wire into a die orifice of substantially the same diameter as said wire, said orifice being flared to a larger diameter at the side thereof into which said wire is introduced, introducing a supply of abrasive granules into said flared portion of said orifice along with said wire, and drawing said wire and said abrasive granules into and through said die orifice whereby a large plurality of generally axially directed grooves are cut in said wire by said abrasive granules, the depth and transverse dimension of said grooves being determined by the size of said abrasive granules and wherein said size is selected as generally of the same order of magnitude as the wave length of visible light radiation produced by said element upon energization thereof.

3. In a method for forming a light producing element for incandescent electric lamps and the like having a roughened and textured light-emitting surface, the steps which comprise forming an elongated metal filament, introducing onto the surface thereof a large plurality of small electrically conductive and light-emitting granules in spaced and randomly oriented disposition on said surface, and sintering said granules to said surface, said granules having a size generally of the same order of magnitude as the wave length of visible light radiation produced upon energization of said element.

4. The method as recited in claim 3 in which said granules and the spaces therebetween are generally of the same order of magnitude as the wave length of visible light radiation produced upon energization of said element.

5. In a method for forming a light-producing element for incandescent electric lamps and the like having a roughened and textured light-emitting surface, the steps which comprise forming an elongated crystalline metal filament, selectively etching away surface portions thereof forming recesses around the borders of individual crystal lattices of like orientation, the depths of said recesses being generally of the same order of magnitude as the wave length of visible light radiation produced upon energization of said element.

6. In a method for forming a light producing element for incandescent electric lamps and the like having a roughened and textured light-emitting surface, the steps which comprise forming an elongated metal filament, introducing onto the surface thereof a large plurality of small electrically conductive and light-emitting granules in spaced and randomly oriented disposition on said surface, and sintering said granules to said surface. the spaces between said granules being generally of the same order of magnitude as the wave length of visible light radiation produced upon energization of said element.

References Cited JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, Assistant Examiner US. Cl. X.R. 

